Hearing aids serve primarily for providing hearing-impaired patients with as natural a hearing sensation as possible and in this regard compensate for usually medically induced malfunctions of the acoustic organs. At the same time, like most medical aids, they have to fulfill this functionality without provoking other adverse effects for their wearer. Adverse effects of said kind can result, for example, from an inappropriate weight of the hearing aid or from, say, restrictions on movement associated with the wearing of hearing aids. Added to this in the case of medical aids that have to be positioned in the region of the face or head is that aesthetic considerations also play a special role. This is particularly true since effort is often aimed at ensuring that the infirmity compensated by the hearing aid should remain hidden from the environment of a patient equipped with an aid of said kind.
The aforementioned requirements are leading to a progressive weight reduction and miniaturization of at least the hearing aid components worn in proximity to the ear. However, there are limits to said miniaturization due to the increasing complexity and functionality of modern hearing aids, which is why multi-component systems have become established in which individual functions of the hearing aid have been exported into an auxiliary device or other components that are to be positioned independently of the ear. In order nonetheless to be able to use these exported functions, at least partial communication is necessary between components of the hearing aid system that are disposed at the ear of the patient and other components which can be arranged at a different location. In particular as a consequence of the demands in terms of comfort that are placed on contemporary hearing aids it follows that said communication between the individual components of a hearing aid system generally takes place wirelessly. This applies in the same way to hearing aid systems comprising a plurality of components which are to be disposed on or in the ears and which are included in a communication connection.
DE 10 2004 047 759 B3 describes a hearing aid which is intended to improve the transmission and amplification of a useful signal in particular in difficult environments, i.e. environments affected by interference signals. Toward that end it is proposed to transmit signals between a first hearing aid worn by a first hearing aid wearer and a second hearing aid worn by a second hearing aid wearer. In this arrangement the transmitted signal can include control parameters, sound field characteristic values or an audio signal. Furthermore it is possible for the signals transmitted between the first hearing aid and the second hearing aid to be transmitted via at least one additional hearing aid worn by at least one additional hearing aid wearer. In this case the third hearing aid fulfills the function of a relay station.
Hearing aid systems within the meaning of the invention are to be understood in the following description to include all multi-component hearing aid systems which comprise at least one component requiring to be disposed on or in the ear of a patient, and which comprise a further component which is communicatively connected at least partially and/or temporarily to the component that is to be worn on the ear. Said further component can be disposed independently of the ear of the patient and/or comprise, in the case of binaural systems, a further component requiring to be disposed on or in the patient's other ear. Included in this context are hearing aids which can be adapted to the personal needs of the respective hearing aid wearer with the aid of a suitable programming device during individual sessions at the practice of a hearing aid acoustician and/or which have auxiliary devices via which the patient him-/herself or another person independent of the hearing aid acoustician can individually adjust or set specific parameters on the hearing aid.
Implicit in the wireless connection concept is that with the exception of systems which can be supplied with energy via inductive couplings, each component of a multi-component hearing aid system must have its own energy source. For components that are worn directly on the or in the ear of a patient it follows from the requirements described in the introduction that an energy source of said kind should be as small and as easy to configure as possible, but on the other hand must possess sufficient capacity to ensure the operational reliability of the hearing aid system over a relatively long period of time without necessitating frequent maintenance measures in the meantime. For this reason hearing aid systems are generally designed in such a way that at least the components of the hearing aid system that are worn directly on or in the ear of the patient are characterized by very low energy consumption. This applies to the maintaining of the functionality as a medical aid just as much as to the implementation of the communication between individual hearing aid components. Standards for inductive wireless transmission of data between individual components of multi-component hearing aid systems have become established for said communication.
With the inductive wireless transmission of data from a hearing aid system component that is to be worn close to the ear to a device equipped with a suitable receiving apparatus, for example an auxiliary device in the form of a relay station, a programming device or a remote control, there is the problem that due to the relatively low capacity, voltage and peak-current-carrying capacity of batteries that are typically used, the maximum transmit power of such hearing aid system components that are to be worn close to the ear is also very limited. This results in a correspondingly short transmission range. An additional factor, in particular for inductive systems that are common today, is that in the near field normally used the reduction in field strength as a function of the distance from the transmitter is of particular consequence. Accordingly, with currently known inductive systems, depending on their design, only distances of approx. 30 cm are spanned on the link from a hearing aid system component designed to be worn on the ear to a receiving apparatus. Due to the low level of the useful signal at the receiving apparatus, even very low-power sources of interference can massively influence the transmission quality or impede or prevent the identification of the data that is to be transmitted.
Due to their very design, however, essential components of a hearing aid system, including auxiliary devices designed to receive data, generate electromagnetic emissions which act as sources of interference during the data transmission and during the data transmission are situated between the individual components in immediate proximity to the transmission link, in particular to the active receiver in each case, i.e. in inductive systems close to the active receiving coil in each case. Sources of interference of this kind are, for example, the inductances of clocked voltage regulators or the supply and output lines of practically all clocked electronic circuits. Circuits of said kind are used for controlling displays, for example. Devices with displays constitute strong emitters overall in this context. In the actual hearing aid, i.e. in components that are to be worn close to the ear, the hearing aid earpiece itself can contribute an additional source of interference.
It is known to shield modules acting as sources of interference. However, effective shielding of magnetic interference fields requires the use of components with relatively large space requirements, for example in μ-metal boxes. In particular in the case of hearing aid components that are to be worn in or on the ear, the necessary space for this is usually not available and the weight disadvantage associated therewith not acceptable.
A sufficiently great distance between the receiving coil and modules acting as sources of interference can likewise not be provided in particular in the case of hearing aid components that are to be worn in or on the ear. With auxiliary devices that are not required to be worn in immediate proximity to the ear, the trend is also toward integration of a high degree of functionality in the device while keeping dimensions to a minimum, so that here too the aim 1s to keep the volume of the modules used as well as their maximum distance from one another as small as possible.
On the assumption that the local arrangement of transmitting and receiving coils and all sources of interference in the hearing aid or in the components of the hearing aid system is fixed and known at least during the data transmission, the receiving coil can in principle be placed in a minimum of the interference field to be expected. Orthogonal alignments of mutually influencing coils and/or interference fields are known for example. It is also known to realize local interference field compensation by generating defined opposing fields. This, however, leads to significant restrictions in terms of design freedom and degree of miniaturization of devices configured in such a manner.